1. Field of the Invention
The present invention relates to a measurement device and, more particularly, to an ultrasonic gas flow measurement device.
2. Description of Related Art
The conventional ultrasonic measurement tube is provided to transmit an ultrasonic signal to the gas filled therein. Since a phase shift may be occurred when the ultrasonic signal passing through the gas, it is able to calculate the flow amount, the concentration and the molecular weight of the gas based on the phase shift between the transmitted and received ultrasonic signals. With reference to FIG. 1, FIG. 1 is a schematic diagram of a conventional ultrasonic measurement tube 1. As shown, the ultrasonic measurement tube 1 includes a transmitter 101, a receiver 102, a gas pipe 103 and a processing unit 104. The gas pipe 103 is a long straight cylindrical tube having an inlet 1031 and an outlet 1032. The transmitter 101 and the receiver 102 are disposed in two sides of the gas pipe 103 respectively. The processing unit 104 is connected to the transmitter 101 and the receiver 102 for controlling the transmitter 101 and the receiver 102, and calculating the phase shift between the transmitted and received ultrasonic signals.
When using the ultrasonic measurement tube 1 to measure a gas, the gas is first applied into the gas pipe 103 from the inlet 1031 for being filled in the gas pipe 103 and then flown out through the outlet 1032. The transmitter 101 transmits an ultrasonic signal in the gas pipe 103. The receiver 102 receives the ultrasonic signal and transfers it to the processing unit 104. The processing unit 104 calculates the phase shift between the ultrasonic signal transmitted by the transmitter 101 and the ultrasonic signal received by the receiver 102.
However, in general, the gas that users want to measure has small flow amount and slow flow speed. Thus, the flow amount and the molecular weight of the gas may be hard to distinguish when flowing into a long straight cylindrical tube as a conventional ultrasonic measurement tube. Furthermore, due to the slow flow speed, the transmitting distance has to be long enough to obtain a recognizable phase shift between ultrasonic signals, and thus the required length of the ultrasonic measurement tube is longer and its volume is accordingly larger. Besides, in the conventional ultrasonic measurement tube, the inlet and outlet of the gas pipe are disposed between the transmitter and the receiver, so that the ultrasonic signal may be influenced by the unstable disturbed flow, resulting in producing echo which is likely to affect the measurement results.
Therefore, it is desirable to provide an ultrasonic gas flow measurement device with a small volume to mitigate and/or obviate the aforementioned problems.